Refrigeration unit for container

Abstract

An oxygen concentration in the interior of a container is detected by an oxygen concentration detection sensor. If the oxygen concentration detected by the oxygen concentration detection sensor is higher than that of a gas mixture, the container is supplied with the gas mixture having an oxygen concentration lower than that of the outside air and higher than a target concentration. The oxygen concentration in the interior of the container is reduced to the vicinity of the oxygen concentration of the gas mixture by supplying the interior of the container with the gas mixture, and then is further reduced to the target concentration by respiration of plants. This appropriately controls the oxygen concentration in the interior of the container, and reduces a decrease in the degree of freshness of the plants.

The invention claimed is: 
     
       1. A container refrigeration apparatus which includes a refrigerant circuit performing a refrigeration cycle, and which is attached to a container that stores plants to cool air in the interior of the container, the container refrigeration apparatus comprising:
 an oxygen concentration detector which detects an oxygen concentration in the interior of the container; and 
 a gas mixture supplier which supplies the interior of the container with a gas mixture having a higher nitrogen concentration and a lower oxygen concentration than outside air, where the oxygen concentration of the gas mixture is higher than a predetermined target concentration, wherein 
 the gas mixture supply device is configured to:
 reduce the oxygen concentration in the interior of the container by supplying the interior of the container with the gas mixture if the oxygen concentration detected by the oxygen concentration detector is higher than the oxygen concentration of the gas mixture; and 
 stop supplying the gas mixture when the oxygen concentration in the interior of the container equals the oxygen concentration of the gas mixture and until the oxygen concentration in the interior of the container is reduced to the target concentration by respiration of the plants absorbing oxygen in the air and releasing carbon dioxide into the air. 
 
 
     
     
       2. The container refrigeration apparatus of  claim 1 , wherein the gas mixture supply device is configured to increase the oxygen concentration in the interior of the container to the target concentration by supplying the interior of the container with the gas mixture if the oxygen concentration detected by the oxygen concentration detector is lower than the target concentration. 
     
     
       3. The container refrigeration apparatus of  claim 1 , further comprising
 an intake portion through which the outside air is introduced into the interior of the container, wherein 
 the intake portion is configured to increase the oxygen concentration in the interior of the container to the target concentration by supplying the interior of the container with the outside air if the oxygen concentration detected by the oxygen concentration detector is lower than the target concentration. 
 
     
     
       4. The container refrigeration apparatus of  claim 1 , further comprising
 an oxygen supplier which supplies the interior of the container with oxygen gas, wherein 
 the oxygen supplier is configured to increase the oxygen concentration in the interior of the container to the target concentration by supplying the interior of the container with the oxygen gas if the oxygen concentration detected by the oxygen concentration detector is lower than the target concentration. 
 
     
     
       5. The container refrigeration apparatus of  claim 1 , further comprising:
 a carbon dioxide concentration detector which detects a carbon dioxide concentration in the interior of the container; and 
 an exhaust portion configured to exhaust the air in the interior of the container out of the container if the carbon dioxide concentration detected by the carbon dioxide concentration detector is higher than a predetermined target concentration. 
 
     
     
       6. The container refrigeration apparatus of  claim 1 , further comprising
 a carbon dioxide concentration detector which detects a carbon dioxide concentration in the interior of the container, wherein 
 the gas mixture supply device is configured to supply the interior of the container with the gas mixture with a higher oxygen concentration than the air in the interior of the container if the carbon dioxide concentration detected by the carbon dioxide concentration detector is higher than the predetermined target concentration. 
 
     
     
       7. The container refrigeration apparatus of  claim 1 , further comprising
 an inert gas supplier which supplies the interior of the container with an inert gas used to reduce the oxygen concentration in the interior of the container without causing an increase in the carbon dioxide concentration in the interior of the container, wherein 
 the inert gas supplier is configured to reduce the oxygen concentration in the interior of the container by supplying the interior of the container with the inert gas before the gas mixture supply device supplies the interior of the container with the gas mixture. 
 
     
     
       8. The container refrigeration apparatus of  claim 7 , wherein the inert gas is nitrogen gas.